Tektronix 2715, Руководство пользователя

Страница: 90 / 360

Dedicated Controls
4–18
2715 User Manual
4. Press [
y
] several times.
The noise is compressed to a grass-like appearance and the indicated sweep
rate increases. The SWEEP [
y
] key increases the sweep rate in a 1-2-5
sequence.
The [
b
] and [
y
] keys perform reciprocal actions; they decrease or increase
the time required to sweep one division. Pressing either key removes the 2715
from the automatic sweep rate selection mode, and [
y
] or [
b
] thereafter
function like the sweep rate selector on a conventional oscilloscope.
NOTE
. Because sweep rate is the inverse of sweep speed, decreasing sweep rate
increases sweep speed.
5. Reset the sweep rate to 50 ms/div and the span/div to 50 kHz.
6. Set the reference level to 38.8 dBmV, and turn on the calibrator.
7. Press [
b
] repeatedly to reduce the time/div.
A beep sounds and the word UNCAL appears.
8. Continue to press [
b
] to increase the sweep speed, and notice the signal
peak decrease and shift to the right.
This condition occurs when sweeping too fast for a given resolution BW and
demonstrates how measurement errors can occur. The resolution filter is
sweeping so fast that its output does not have time to reach steady-state.
9. Reselect ZERO SPAN.
The UNCAL message disappears, because in the zero span mode the filter is
not being swept at all.
10. Reset the displayed sweep speed to 1 ms/div.
AUTO.
The AUTO key in the SWEEP function block serves two purposes. First,
it is used in much the same way as the AUTO key in the RES BW function
block — as a toggle-action key that switches the 2715 between automatic and
manual selection of sweep rate. When AUTO sweep rate selection is active, the
sweep rate selected by the 2715 depends on the span/div, resolution bandwidth,
and video filter in use. Second, pressing the SWEEP AUTO key when the 2715
is in the single sweep mode exits from that mode.
11. Press [ZERO] to exit the zero span mode.
Notice how distorted the calibration signal is.